Evaluation of transdermal fentanyl patch attachment in dogs and analysis of residual fentanyl content following removal

Objective To investigate whether the method used to attach matrix-type fentanyl patches influences the degree of skin attachment and the amount of active drug remaining in patches after use. Study design Prospective. randomised clinical study. Study population Fifteen adult dogs of mixed breeds. Methods Two equally sized matrix-type fentanyl patches were attached to the dorsal third of the lateral thorax of fifteen dogs for 72 hours. The two patches were attached using different techniques: Method AD used an adhesive dressing in combination with a transparent film. Method TO used tissue adhesive applied to the edges of the patch. After 72 hours the patches were removed and the proportion of the patch attached at this time calculated. The residual content of the patches was analysed using a validated gas chromatography mass spectrometery (GC MS) analysis technique. Results After 72 hours of continuous attachment, the mean proportion of drug uptake for method AD was 17.2 (SD +/- 11.1)% and for method TG this was 16.9 (SD +/- 7.3)%. The median proportion of attachment for method AD was 100% and for method TO was 95.6%. Conclusions The method of attachment did not significantly influence the uptake of fentanyl from matrix-type patches. The method of attachment resulted in a significant difference in the proportion of the patch attached 72 hours after placement. with method AD resulting in a greater median proportion of attachment than TO. Clinical relevance The method used to attach matrix-type fentanyl patches to dogs should not interfere with drug uptake. The residual fentanyl content remaining in these patches after 72 hours of continuous application is significant and could lead to intoxication if ingested by humans.